"4 x 800M on 2 Min" Means run an 800, rest two minutes, then run another one, 4 times. This is a form of interval training that is referred to in strength training as "density training", where you do X number of reps of an exercise (pullups for instance) every minute for Y minutes. In this example, a density protocol for (4 @ 1) x 20 would mean: do 4 pullups, hit your stopwatch, at the 1 minute mark do another 4 pullups, repeat, ad nauseam, until you eventually have done your 20 sets.

As far as pace goes, read the footnote on p.388 for Interval Training. Basically go 85-90% so that your working your butt off and hitting your anaerobic capacity, but still recovering enough in the two minute rest period to hit within 3 seconds (+ or -) of your last time on your next run.